Drop Experiments with Concentration Gradient

170215 anpf evas-cell-with-gradient enIn the ReDrop simulation tool for the design of extraction columns individual drops are followed by modelling the different effects acting on them. Two effects are of special importance, namely sedimentation, i.e. drop velocity determining the residence time and thus the contact time for mass transfer, and mass transfer, which determines the efficiency of the extraction column. It has been shown previously that sedimentation and mass transfer are interlinked. Especially during the first seconds of mass transfer, the concentration gradient at the interface is high, which may induce interfacial instabilities. These instabilities in turn lead to an increase in flow resistance, slowing down the drops.

In order to characterize drop sedimentation and mass transfer, we use single-drop experiments, which allow us to characterize all influences stemming from the specific material system investigated. In the sedimentation cell, drops of defined volume are generated with a computer-driven syringe and a nozzle and the rising or sinking velocity evaluated from videos recorded. Mass transfer is characterized in a dedicated cell, where the identically produced drops enter a conical part with a counterflow of the continuous phase. In this counterflow, they are levitated at a certain position, where mass transfer can take place for a defined time. After the desired contact time has been reached, the counterflow is stopped and the drop moves on, is collected with a funnel, and the fluid can then be analyzed.

In the mass-transfer cell, the continuous phase has essentially constant composition, which does apparently not correspond to the actual situation in an extraction column, where the drop is moving along the column through the concentration profile that has developed. Thus in this project the interaction between sedimentation and mass transfer is investigated more closely as well as the influence of a concentration gradient on both. This is realized in a modified single-drop cell, which is shown in the Figure. A defined concentration profile can be established in that cell, which is stable for an extended time to allow systematic investigation of the behavior of drops passing through this concentration gradient.

 

Contact: Dipl.-Ing. Eva Kalvoda (supervised at TU Graz)

Supervisor: Prof. Dr.-Ing. Andreas Pfennig, andreas.pfennig@ulg.ac.be

Funded by: own funding

 

Publications:

 

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